The neural crest of vertebrates gives rise to a diverse array of cell types, including neurons and glia of the peripheral nervous system, head and neck cartilage, and pigment cells. In humans, the neural crest is the target of a number of developmental abnormalities as well as cancers, collectively referred to as neurocristopathies. To better understand the mechanisms of neural crest cell fate specification and differentiation, we have undertaken studies of this system in the zebrafish. We have identified a zebrafish gene required for development of neural crest-derived melanin-producing pigment cells, known as melanophores. Zebrafish homozygous for mutations at the nacre locus lack all melanophores from embryonic through adult stages, but have normal eye pigmentation and development of other neural crest derivatives. In this proposal I describe the following experiments to clarify the role of nacre in melanophore development: the nacre defect will be characterized at the cellular level by cell labeling and transplant studies. To identify potential candidate genes nacre will be placed on the genetic linkage map. The role of the zebrafish homologue of the microphthalmia-associated transcription factor (Mitf), a known pigment cell regulator in mice, in melanophore development will be investigated by misexpression in wild-type and nacre embryos. The proposed research will extend our understanding of the specification and differentiation of pigment cells in vertebrates and shed light on human conditions in which these processes are disrupted, such as piebaldism and melanoma.